Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio of a charged molecule or molecule fragments formed from a sample. MS is used to analyze the mass, chemical composition, and/or chemical structure of a sample of interest. In general, MS includes three steps: ionizing a sample to form charged molecules or molecule fragments (i.e., ions); separating the ions according to their mass-to-charge ratio; and detecting the separated ions to form a mass-to-charge signal (i.e., spectra).
There are many different types of MS devices. For example, sector, time-of-flight, quadrupole, ion trap, Fourier transform ion cyclotron resonance, and tandem (two or more of the above combined in tandem or orthogonal) mass spectrometers are all different instruments that are considered to be MS devices. Each device has its own limitations with respect to the analysis and obtained spectra of samples. Certain characteristics of MS analysis include, e.g., mass accuracy, resolution, sensitivity, dynamic range, selectivity, and specificity etc.
MS data analysis is a complicated subject, in which the degree of accuracy of data interpretation on mass, chemical composition, and chemical structure is limited by one or more of the above analysis characteristics of the instruments and/or operational methods utilized. Typically, an ion mobility spectrometer is composed of an ionization source, a drift cell and an ion detector. Instruments of these types allow for separation and analysis of ions according to their mobility and mass-to-charge ratio (m/z) in a gas phase, which in turn adds one additional dimension of separation. This added dimension of separation is beneficial for the identification of molecules of interest. The challenging issue, however, has been to effectively discriminate and take advantage of downstream non-parent ions to improve the overall sensitivity, selectivity, specificity, and/or dynamic range of a sample.
One such method for improvement deals with, for example, enhancing the sensitivity and/or selectivity in Matrix-Assisted Laser Desorption/Ionization (MALDI) experiments for structural elucidation of samples. During a MALDI experiment, there are three types of ions formed: stable ions with insufficient excitation energy to dissociate before detection, e.g., precursor or parent ions; unstable ions with enough energy to dissociate before leaving the ionization source, and metastable ions with intermediate energy which decomposes in transit. Typically, in this experiment, a sample is ionized and the resulting ions are separated by their mass-to-charge ratios in an analyzer.